This invention relates generally to digital signal manipulation, and more particularly to an apparatus, a method and a system to transcode matching pursuit-coded digital signals (e.g., audio, image, video) in a gateway (i.e., transcoding proxy).
New classes of pervasive computing devices such as personal digital assistants (PDAs), hand-held computers (HHC) and smart phones give users more ubiquitous access to information than ever. Many of these devices have capabilities to serve as calendar tools, address books, web browsers, etc. As users are beginning to rely more heavily on pervasive computing devices, there is a growing need for applications to bring multimedia information to these devices. However, due to heterogeneous device capabilities, in terms of display size, storage, processing power, and network access, there are new challenges for designing appropriate tools that allow these devices to effectively access, store and process multimedia information. Concurrent with the developments in pervasive computing, advances in storage, networking, and authoring tools are driving the production of large amounts of rich multimedia content. The result is a growing mismatch between the available rich content and the capabilities of the client devices to access and process it.
Many researchers have been working on adapting multimedia content in so-called transcoding proxies. Transcoding proxies are typically located in access providers. Video transcoding includes spatial scaling (image size), temporal scaling (frame rate), rate reduction, and spatial rotation and translation. A good transcoding algorithm maximizes the trade-off between transcoding quality (quality of the manipulated signal) and related processing power. Processing power is indeed an issue in order for an access provider to scale to the demand, which is the reason why only compressed domain transcoding is viable.
The most cited multimedia standards for compression create bit streams that are delicate to manipulate in the compressed domain. A good transcoding quality implies a high processing power. Moreover signal manipulation is limited.
What is needed, therefore, and what is an objective of the present invention, is to provide an apparatus, method and system for transcoding signals in the compressed domain.
It is another objective of the present invention provides an apparatus, a method and a system to efficiently adapt the bit rate and manipulate, in the compressed domain, spatial and/or temporal scaling of matching pursuit coded digital signals.
Yet another objective of the invention is to provide the foregoing manipulations, usually referred to as transcoding, at an origin server or at any intermediary along the transmission path from the origin server to the client device, including at the client device.
The foregoing and other objectives are realized by the present invention comprising an apparatus, a method and a system to efficiently manipulate, in the compressed domain, spatial and/or temporal scaling of matching pursuit coded digital signals. The transcoding may take place at an origin server, in any intermediary along the transmission path from the origin server to the client device, or in the client device. The preferred embodiment focuses on a method to perform rate adaptation and spatial and temporal scaling of a video stream composed of atoms output by matching pursuit coding of digital signals in order to serve a set of heterogeneous client devices (e.g., a high-end personal computer, a personal digital assistant and a wireless phone). The proposed preferred method is implemented in a transcoding proxy sitting in an intermediary node along the transmission path. The same strategy applies to 1-D atoms (decomposition of audio signals) and 2-D atoms (image decomposition).